MATL 341 Exam 2

At any given temperature, order from best to worst the tensile properties of different materials

Nickel, Stainless Steel, Alloy Steel, Carbon Steel

What happens to the amount of oxidation (weight gain) as temperature goes up?

Goes up

True/False: Tensile properties at high temperatures are time dependent.

True (High temp deformation process is called creep)

Definition of Creep

The progressive deformation of a material at a constant stress (often below the yield strength) occurring at elevated temperatures

What are the 3 Stages of Creep

1. Primary Creep

2. Secondary Creep (steady state)

3. Tertiary Creep

Failure occurs via grain boundaries at specific temperatures

What is the maximum use temp of polymers?

550 F

What is the maximum use temp of metals?

1800 F

(has a large range)

What is the maximum use temp of ceramics?

3000 F

Which materials are good at a service temperature of 300-750 F?

Copper > Magnesium > Aluminum

Which materials are good at a service temperature of 750-1000 F?

Carbon Steels > Low Alloy Steels & Titanium

Which materials are good at a service temperature of 1000 - 1400 F?

Stainless Steels

Which materials are good at a service temperature of 1400 - 1800 F?

Nickel & Cobalt Alloys

Which materials are good at a service temperature of 1800+ F?

Molybdenum > Tantalium > Tungsten

Definition of Corrosion

The process of a refined metal returning to its lowest energy state (natural state)

Define Corrosion Resistance

Ability of a metal to resist deterioration by chemical reactions

3 Requirements for Corrosion

1. Anode (corrodes)

2. Cathode (protected)

3. Electrolyte (fluid)

8 Types of Corrosion

1. Uniform

2. Pitting

3. Crevice

4. De-Alloying

5. Galvanic

6. Intergranular

7. Erosion

8. Stress Corrosion: Cracking

What is Uniform Corrosion?

Total attack of the surface

What is Pitting?

Highly localized corrosion of specific areas

What is Crevice Corrosion?

Corrosion due to a crevice, which by its design changes the localized environment and creates a chemical potential difference

What is De-Alloying?

One of the components in an alloy corrodes leaving behind a porous residue

What is Galvanic Corrosion?

Dissimilar metals coupled electrically in the presence of an electrolyte

What is Intergranular Corrosion?

Corrosion which occurs in the grain boundaries of a material (in SS chromium wants to be with carbon)

What is Erosion Corrosion?

Combination of corrosion and wear due to contact with a flowing liquid, solid, or gas

What is Stress Corrosion Cracking?

Combination of tensile stresses and a corrosive environment which causes brittle fracture to occur at stress levels below the UTS of the material

What is the Inspection Corrosion Protection Technique?

Design for inspection of troublesome corrosion areas and design in wear plates for known areas of excessive corrosion

What is the Galvanic Corrosion Protection Technique?

-Decouple anodes and cathodes with non-conductive materials (have a sacrificial anode)

-Externally apply a current

What is the Crevice Corrosion Protection Technique?

-Avoid incomplete weld penetration as it may result in a crevice

-Avoid stagnant liquid areas

What is the application of austenitic stainless steels?

-Low strength

-Good/excellent corrosion resistance

-2XX & 3XX series

What is the application of ferritic stainless steels?

-Low strength

-Low/moderate corrosion resistance

-4XX series

What is the application of martensitic stainless steels?

-Good/excellent strength

-Low/moderate corrosion resistance

-4XX & 5XX series

Definition of wear

Unintentional damage to surfaces, generally involving progressive loss of material, due to relative motion between the surfaces and contacting substance or substances

4 Primary Wear Mechanisms

1. Adhesion

2. Abrasion

3. Surface Fatigue

4. Erosion

Definition of Erosion

Progressive loss of material from a solid surface due to a relative motion between solid/fluid, solid/multi-component fluid, impinging liquid, or solid particles

5 Types of Erosion

1. Solid Particle (solid carried by a gas)

2. Slurry (solid carried by a fluid)

3. Liquid Impact (outside liquid smacks material)

4. Liquid (inside liquid breaks inside oxide)

5. Cavitation (implosion of bubbles)

Definition of Adhesion

Progressive loss of material due to localized bonding between contacting solids leading to material transfer or loss from one or both solids

4 Types of Adhesion

1. Galling/Seizure (single high stress event)

2. Scuffing & Scoring (moderate form- scratches in direction of motion)

3. Oxidative (mild form- oxide regions form due to contact in air)

4. Fretting (oscillatory rubbing motion)

Definition of Abrasion

Unintentional wear produced by hard sharp particles (abrasive) plowing (deformation) or removing surface material of a softer surface

4 Types of Abrasion

1. Low Stress (fine scratches)

2. High Stress (fracture of abrasive)

3. Gouging (deep scratch)

4. Polishing (least aggressive)

Definition of Surface Fatigue

Deformation of a surface and/or cracking of the subsurface of a component due to applied loads, typically followed by ejection of surface fragments

4 Types of Surface Fatigue

1. Pitting (localized- most common)

2. Impact (repeated impacts)

3. Spalling (loss of surface due to thermal/mechanical fatigue)

4. Brinelling (static overload)